In the production of malt fermented beverages such as beer, happoshu (low-malt beer), whisky, etc., the major three sugars contained in wort prepared by mashing malt, etc. are glucose, maltose and maltotriose. The ratio of these malt-derived sugars can be somewhat varied depending on the mashing process but does not change significantly without addition of enzyme preparations, glycosylated starch, etc., which may be approximately 1:5:1. Among them, glucose is a monosaccharide and preferentially assimilated as a sugar most favored by yeast. Yeast has numerous genes suppressed in the presence of glucose during the transcription process. This control mechanism is called glucose repression. Several transporters required for uptake of maltose or maltotriose into yeast all undergo this repression. It is known that some of these gene products which undergo the gene repression are further inactivated in the presence of glucose after translation. Maltose transporters are also within this type and known to be rapidly degraded in the presence of glucose. The first step of assimilation of maltose or maltotriose is the uptake into yeast cells by these transporters and, when transporters are degraded, assimilation stops. This is the reason why the expression of transporter is called a rate-determining step.    Non-Patent Literature 1: Brondijk, T. H., van der Rest, M. E., Pluim, D., de Vries, Y. de., Stingl, K., Poolman, B., and Konings, W. N. (1998) J. Biol. Chem., 273 (25), 15352-15357    Non-Patent Literature 2: Medintz, I., Wang, X., Hradek, T., and Michels, C. A. (2000) Biochemistry, 39 (15), 4518-4526    Non-Patent Literature 3: Gadura, N., and Michels, C. A. (2006) Curr. Genet., 50 (2), 101-114    Non-Patent Literature 4: Han E. K., Cotty F., Sottas C., Jiang H., Michels C. A., (1995) Mol. Microbiol., 17(6), 1093-107
Accordingly, when a glucose concentration is high, for example, Agt1p in yeast cannot efficiently function upon incubation since its degradation rate is very rapid in the presence of glucose, which is considered as one of the problems.